There is available a vehicular automatic transmission provided with a hydraulic control unit configured to perform a switching operation depending upon a selected shift lever position to effect a shifting operation, according to an electric command signal fed through a wire (electric wire) called a shift by wire (SBW). A rotary motion of such an output shaft of an automatic transmission is inhibited by an actuator of a parking lock device, which is operated on the basis of a command signal generated by a shift lever operation to a parking position (P). Patent Document 1 discloses a technique wherein the actuator of the parking lock device is hydraulically operated.
According to the technique disclosed in Patent Document 1, the parking lock device is brought into its locking state by a biasing force of a spring, to inhibit the rotation of the output shaft, while the parking lock device placed in the locking state is brought into its unlocking state, by a force produced by a hydraulically operated valve, to permit the rotation of the output shaft.    Patent Document 1: JP-2002-533631